1. Field of the Invention
The present invention relates to a heat treatment apparatus for heat treating a target substrate, such as a semiconductor wafer, and more particularly, to a hot-wall type vertical heat treatment apparatus.
2. Discussion of the Background
In the manufacture of semiconductor devices, various heat treatment apparatuses are used in order to apply various treatments, such as oxidation, diffusion, CVD, and so forth, to semiconductor wafers, i.e., the target substrates. As one of such heat treatment apparatuses, there is known, for instance, a single-substrate-processing type in which, a lord-lock chamber, i.e., a preparatory vacuum chamber connected to a treatment chamber, i.e., a heat treatment furnace, is disposed, and, in this preparatory vacuum chamber, a wafer transfer mechanism is provided. In the case of this heat treatment apparatus, by previously setting the interior of the lord-lock chamber at approximately the same pressure as that in the heat treatment furnace, a wafer can be transferred in and out of the heat treatment furnace by opening the furnace throat without resetting the pressure in the heat treatment furnace to the atmospheric pressure; and thus, the shortening of the required time and the improvement in throughput can be realized.
By the way, the transfer mechanism etc. are directly mounted in the preparatory vacuum chamber. In case that the heat treatment furnace is of the so-called cold wall type in which a wafer is directly heated by lamp heating or the like, the preparatory vacuum chamber is hard to be thermally affected from the heat treatment furnace. Accordingly, even if the transfer mechanism is directly mounted in the preparatory vacuum chamber, such an arrangement does not cause problem so much.
However, in case that, in the heat treatment apparatus, the heat treatment furnace is of the so-called hot-wall type in which the peripheral surface of the reaction tube is surrounded by a heater wire and a heat insulation layer to heat the whole interior of the furnace, the preparatory vacuum chamber is thermally affected by the radiant heat when the thermally treatment furnace is opened. Therefore, where the transfer mechanism is mounted directly in the preparatory vacuum chamber, the axial position of the transfer mechanism is deviated due to the strain or deformation of the preparatory vacuum chamber which has been thermally affected; and thus, there is the fear that the matching accuracy may become deteriorated. Further, in order to assure the matching accuracy of the transfer mechanism, it is necessary to machine the preparatory vacuum chamber with a high accuracy, which results in increasing the manufacturing costs, this being a problematic matter, too.